1. Field of the Invention
The present invention relates to a confocal microscope.
2. Description of the Related Art
Diagnosis and research of diseases require observation of a thick specimen such as a biological sample for a structure in a thickness direction (depth direction). In observation of such a thick object through a normal microscope, light from planes other than a focal plane is adversely superimposed as blur on the focal plane. This makes it difficult to accurately observe the structure in the thickness direction.
For this reason, a confocal microscope has been conventionally used. The confocal microscope includes a pinhole and detects only light passing through the pinhole. Thus, the pinhole needs to have an appropriate size to obtain a sufficient light quantity for observation. However, a larger pinhole degrades resolution. M. Gu, “Principles of Three-Dimensional Imaging in Confocal Microscopes”, World Scientific, 1996, pp. 47-149 discloses a configuration for improving the depth-directional resolution by introducing a ring zonal (an annular) shaped pupil of a collection optical system of a confocal microscope. Japanese Patent Laid-open No. H2-247605 discloses a method using an annular mask disposed at the pupil position of a collection optical system to allow a depth of focus to be varied.
In addition, a confocal microscope that varies the depth-directional resolution by using a multi-pinhole array is known. International Publication No. WO 2002/068903 discloses a configuration in which the depth-directional resolution is variable by varying the numerical aperture of a collimating lens.
However, the use of a larger pinhole to obtain a sufficient light quantity degrades the depth-directional resolution. On the other hand, the use of the multi-pinhole array requires Koehler illumination to keep an illumination light intensity uniform. In this case, a pinhole having a finite size is illuminated with a partially coherent light, which results in considerable influence on the resolution by spatial coherence of the illumination light on a surface of the pinhole. Thus, the resolution needs to be improved based on quantitative understanding of the spatial coherence on the surface of the pinhole.